1. Field of the Invention
This invention relates to an overhead door suspended from the top of an opening of a cabinet or the like and capable of being lifted until it is placed on the roof wall of the cabinet to keep the door open.
2. Prior Art
FIG. 9 of the accompanying drawing illustrates a known overhead door a designed to be lifted and placed under the roof wall c of a cabinet main body b (Japanese Utility Model Publication No. 60-18528).
A known overhead door of the above-described type is, however, accompanied by a number of drawbacks including that it has a rather complicated configuration comprising a support rod d and a short rod e arranged for swinging the door a up and down as well as a spring f fitted thereto, a slide assembly constituted by a slide rail g and a door wheel h is arranged within the cabinet main body to make it rather cumbersome to secure the door a to a cabinet main body b and positionally adjust the door a once it has been secured to the cabinet main body b and that the space available within the cabinet b is limited because it has to accommodate the door a within it.
Additionally, when the door a is opened, the cabinet becomes esthetically unattractive because of the exposed support rod d and spring f and, during the operation of opening or closing the door, the finger of the user operating the door may be accidentally caught and pinched by the spring f or between the spring f and the support rod d.
In view of the above identified problems and other problems of known overhead doors of the type under consideration, the inventor of the present invention has proposed an overhead door as illustrated in FIG. 8 of the accompanying drawings.
With the illustrated arrangement, a support arm k is pivotably fitted at an end to the inner surface of each lateral wall of a cabinet main body or the like by way of or without a damper j and at the opposite end to the rear surface of a door m by means of a pin n at a position close to the lower edge of the door. On the other hand, the door m is swingable fitted to the front edge of the roof plate p of the cabinet main body by means of hinges r so that it may be moved between a fully closed position for completely closing the cabinet and a raised position where it rests on the roof plate p to fully open the cabinet through its swinging and sliding motion realized by using a pair of slide rail assemblies q, each of which comprises an inner rail u and an outer rail v. At the same time, a pair of vertical grooves s are formed on the rear surface of the door m to respectively accommodate a pair of tension springs t, each of which is secured at the opposite ends to the upper end of the corresponding hinge r and the lower end s' of the groove s in order to urge the outer rail v and the door m upward relative to the inner rail u of the slide rail assembly q.
The above arrangement is, however, still accompanied by a problem as described below.
As the door m is pulled downward from the open position to swing down to the closed position, the tension springs t are expanded to show a length four times as long as their contracted length for the door in a fully open state. Since the door m is made open for about 8 hours a day in average and remains closed for the rest of the day, the time during which the tension spring t is expanded is by far longer than the time when it remains in a contracted state so that consequently the service life of the tension springs may be undesirably short.
In view of the above problem, it is therefore an object of the invention to provide an overhead door of a cabinet or the like equipped with a pair of slide rail assemblies as described above by referring to FIG. 8 and also with a pair of stays, each having its base end rotatably fitted to the inner surface of a corresponding lateral wall of a cabinet to which the door is linked and its front end pivotably fitted to the rear surface of the door at a position close to the lower edge of the door, and a pair of stay holding tension springs provided for the respective stays, each extending between a middle point of the corresponding stay and an appropriate position on the inner surface of the corresponding lateral wall of the cabinet, so that the stay holding tension springs may be expanded to a length only twice as long as their contracted length in order to improve their service life and ensure the door to operate smoothly for opening and closing for a prolonged period of time, while the door and the attachments may not provide any obstacle for the operation of storing and retrieving objects in and from the cabinet once the door is swung upward for opening and placed on the roof plate nor the stay holding tension springs may expand out of the opening of the cabinet to accidentally pinch a finger tip of the user.
An overhead door according to the invention may be equipped not only with stay holding tension springs as described above but also with a pair of grooves arranged on the rear surface for accommodating the respective door holding tension springs as in the case of the above described prior art overhead door so that the tension springs may not move out from the door during opening and closing operations. With such an arrangement, the risk for the stay holding tension springs of accidentally pinching a finger tip of the user can be effectively eliminated when the door is being opened or closed and the operation of opening and closing the door proceeds smoothly and slowly without requiring substantial force on the part of the user because of the joint effect of the door and stay holding tension springs. Additionally, the service life of the door and stay holding tension springs can be considerably expanded as the load of moving the door is borne by all of them.
Alternatively, the door may be movably held to the adjacent lateral walls of the cabinet not simply by means of respective stays having their ends pivotably secured to the lateral walls and the door but by way of a damper disposed between the base end of each of the support arms and the related lateral wall so that, when the door is closed from the open position where it is located on the roof wall, it is moved only slowly and softly due to the resistance or the damping effect of the damper against the torque of the door produced by its load.
Preferably, an overhead door according to the invention may be provided with a combination of dampers and door and stay holding tension springs arranged at appropriate locations so that both the braking force of the dampers and the restoring force of the expanded springs may be exploited to decelerate the speed and lessen the load with which the door is swung open or closed and consequently no substantial effort is required for the user to open or close the door.
Alternatively, an overhead door according to the invention may be provided with a combination of dampers and coil springs arranged at appropriate locations so that both the braking force of the dampers and the restoring force of the coil springs may be exploited to decelerate the speed and lessen the load with which the door is swung open or closed and consequently no substantial effort is required for the user to open or close the door.
Still alternatively, an overhead door according to the invention may be provided with a combination of dampers, door holding tension springs and coil springs arranged at appropriate locations so that all the braking force of the dampers, the restoring force of the expanded springs and the coil springs may be fully exploited to further decelerate the speed and lessen the load with which the door is swung open or closed and consequently no substantial effort is required for the user to open or close the door.